The present invention relates to high performance, photoimageable resin compositions useful for the manufacture of printing plates. In particular, the present invention relates to compositions which exhibit excellent processing characteristics when deposited on a printing plate, e.g., exceptional physical properties, high rate of cure upon exposure to radiation, high resolution, and the like. In accordance with another aspect, the present invention relates to methods for the preparation of formulations comprising invention compositions and methods for use thereof.
Flexographic printing is widely used in the production of newspapers and in the decorative printing of packaging media. In flexographic printing, a layer of a flexible printing medium is deposited onto a flexible substrate such as a thin sheet of steel, aluminum, or synthetic polymer, to form a printing plate. A relief pattern corresponding to the negative image to be printed is formed in the printing medium. The plate is then mounted on the printing press, and printing commences.
One type of printing medium is natural or synthetic rubber. This printing medium has excellent mechanical properties, but the preparation of a printing plate with a rubber printing medium is slow and of low quality. For molded rubber plates, a pattern plate and a matrix board are prepared, and rubber plates are then hot press molded. Molded rubber printing media are not practical for printing applications with short deadlines, such as newspapers. Due to the nature of the medium and imaging techniques described above, photosensitive printing plates have been developed to meet the demand for fast, higher resolutions and long press runs.
The use of a photosensitive printing medium for the manufacture of flexographic printing plates is described in general terms as follows. The photosensitive printing material is coated onto the substrate to form the printing plate. The coated side is exposed with light through a photographic negative of the image to be printed, causing photopolymerization of the exposed portion of the printing medium, which then becomes physically hardened and resistant to solvent removal. The unexposed and therefore unhardened portion of the printing medium is removed by washing with solvent, leaving a relief pattern of the image to be printed. The printing plate is mounted on a press and printing commences.
Non-flexographic printing plates such as letterpress plates are also used for printing newspapers, shoppers, and books. Photosensitive resin compositions have been developed for use with non-flexographic printing applications for the same reasons disclosed above for flexographic applications. The use of photosensitive printing media for the manufacture of letterpress printing plates is essentially the same as described above for flexographic printing applications.
Photosensitive resin compositions currently employed for the preparation of photosensitive resin plates can be based on unsaturated polyesters, polyvinyl alcohols, polyamides, cellulose acetate succinates, polydiene polymers and their copolymers, urethanes, etc. Currently available photosensitive resin compositions are adequate in the manufacture of flexible printing plates. However, due to the rapid growth of the printing industry, there is an ever-increasing demand for photosensitive resin compositions with improved performance and processing characteristics. The resin composition must maintain a good balance between mechanical properties such as resilience, hardness and toughness. Additionally, in order to increase manufacturing efficiency, the resin will desirably exhibit reduced tack for ease of handling before photopolymerization and will also desirably photopolymerize as quickly as possible when exposed to the photoinitiation source.
Accordingly, there remains a need in the art for photosensitive resin compositions having improved chemical and physical properties. The present invention fulfills this need and further provides related advantages.
In accordance with the present invention, there are provided high performance, photoimageable resin compositions having excellent physical properties, e.g., resilience, hardness, toughness, and the like, as well as high rates of cure upon exposure to radiation. In a further aspect of the invention, there are provided printing plates prepared employing invention compositions, wherein said printing plates are characterized as having excellent exposure sensitivity, the capability of rapidly curing upon exposure, excellent retention of fine details, excellent colorless performance (i.e., provides high quality color printing), and the like. Moreover, printing plates prepared employing invention compositions have good flexibility, excellent washout properties, and retain such properties over extended periods of storage. In another aspect of the invention, there are provided methods for the preparation of formulations comprising said compositions and methods for use thereof.
A desirable characteristic of any printing medium is developability in water, rather than organic solvents. Water-developable compositions are desirable for such reasons as ease of handling, health of workers who are in contact therewith, safety, and avoidance of environmental pollution. Therefore, in accordance with a particular aspect of the invention there are provided water-developable formulations comprising invention compositions with improved physical properties and increased rates of cure upon exposure to radiation.
Additionally, due to the improved physical properties provided by invention compositions, printing plates prepared employing such compositions have excellent form stability, thereby enabling such plates to be handled without the need for excessive care. Once photopolymerized, invention printing plates have excellent physical properties, enabling their use in many very demanding commercial applications, e.g., publication printing, and other long-run applications. Such applications require the photopolymerized resin to have excellent water resistance (so that exposure to water-based inks does not significantly alter resin properties), as well as good resilience (so that the physical contacting associated with the printing process does not significantly degrade resin properties). Photopolymerized compositions of the invention maintain a good balance between toughness, resilience, and hardness. Photopolymerization of invention compositions yields products with ink transfer characteristics considered very good by flexographic printing standards and demonstrates sufficient toughness for extended printing runs as required in such areas as directory, newspapers, and pre-printed inserts. In addition, the increased image resolution provided by invention compositions leads to printing plates with higher print quality.